This invention relates to an air exchanger for replacing indoor air in an enclosure with outdoor air and, more particularly, to an air exchanger which includes a heat exchanger which changes the temperature of the outdoor air as it enters the building to a temperature approaching that of the indoor air temperature.
In recent years there has been an increased emphasis on energy conservation in homes and other buildings in response to increasing fuel costs and decreasing and less readily available worldwide fuel supplies. This emphasis has included efforts to make residential and commercial buildings increasingly energy efficient such that less electricity and heating fuel are required to heat and cool them. Such efforts have included, for example, providing highly insulating multiple pane windows and doors, increasing the insulation ratings in walls, attics and ceilings, providing unique outer wall constructions having closed insulating air gaps, and incorporating radiant energy reflecting materials in buildings. These efforts have substantially reduced energy consumption by decreasing heat transfer between the interiors of the buildings and the outdoors.
Despite the beneficial energy conservation that has been achieved by these efforts, they have at the same time created a number of undesirable and potentially hazardous effects. More particularly, by making buildings more energy efficient by reducing air leakage around windows, doors and other areas, healthful air circulation between the indoors and the outdoors has been significantly reduced. Consequently, the indoor air has become increasingly stale due to a significant increase in the levels of dirt, mold, bacteria, fungus, dust, carbon, nitrogen, radon, and other contaminants which have consequently created unhealthy indoor environments. These undesirable effects have been most pronounced in the colder regions of the United States and in other cold-climate countries, where efforts to decrease energy consumption have been most highly concentrated. Accordingly, in these places, the levels of indoor contaminants have been especially high and have raised the most serious health concerns.
In light of the simultaneous goals of energy conservation and maintaining healthy indoor environments, a number of attempts to make efficient air-to-air heat exchangers have been made. See Energy Design Update, "Air-to-Air Heat Exchangers,"1987 Cutler Information Corp. There is still a need for an air exchanger which is energy efficient and comprises a heat exchanger having a high heat transfer efficiency so that it is capable of continuously supplying fresh outdoor air into a room at a temperature approaching the indoor temperature to minimize any subsequent indoor heating or cooling effects. The air-to-air heat exchanger must provide a significant air exchange without loss of heat and without creating negative pressures inside the home or building.
Most heat exchangers require some form of a means to prevent frost from forming and/or defrost the heat exchanger if it does form. Most commonly electric heaters are used to either preheat cold air prior to entering the heat exchanger or to defrost the cores when frost accumulates. Timers occasionally supplemented with external temperature sensors are often used to initiate the defrost heaters. These methods consume a large amount of energy and when timers are used may be energizing the heaters unnecessarily. The heat exchanger disclosed utilizes the waste heat from the blower motors and dampers to defrost the heat core. Further, the dampers are actuated by means of a pressure switch.
Such an air exchanger would provide needed air circulation to assure healthy home and workplace environments that, to date, have been sacrificed at the expense of increased energy conservation, without detracting from the energy conservation gains that have been made.